A neoplasm ("new growth"), or tumor, is an abnormal mass of cells. A neoplasm may be benign or malignant (cancerous). A benign ("kind") tumor tends to grow slowly, and its cells stay together. Because benign tumors form masses with distinct borders, they can usually be removed surgically.
A malignant ("wicked") neoplasm, or cancer, usually grows much more rapidly and invasively than a benign tumor. In fact, two basic defects in behavior that characterize most cancer cells are rapid multiplication and abnormal relations with neighboring cells. Unlike normal cells, which respect one another's boundaries and form tissues in an orderly, organized manner, cancer cells grow helter-skelter on one another and infiltrate normal tissues. They are apparently no longer able to receive or respond appropriately to signals from surrounding cells; communication is lacking.
When a cell that has transformed into a cancer cell multiplies, all the cells derived from it are also abnormal. Unlike the cells of benign tumors, cancer cells do not retain normal structural features. Cancers that develop from tissues or muscle are referred to as sarcomas. Those that originate in epithelial tissue are called carcinomas. Most human cancers are epithelial.
Death from cancer almost always results from metastasis, a migration of cancer cells through blood or lymph channels to distant parts of the body. Once there, they multiply, forming new malignant neoplasms that can interfere with the normal functions of the tissues being invaded. Cancer often spreads so rapidly and extensively that surgeons are unable to locate or remove all the malignant masses.
Studies suggest that many neoplasms grow to several millimeters in diameter and then enter a dormant stage, which may last for months or even years. Some reasearchers hypothesize that eventually cells of the neoplasm release a chemical substance that stimulates nearby blood vessels to develop new capillaries that grow into the abnormal mass of cells. Nourished by its new blood supply, the neoplasm may begin to grow rapidly. Newly formed blood vessels have leaky walls and so are an important route for metastasis. Malignant cells enter the blood through these walls and are transported to new sites.
Cancers appear to arise when a cell accumulates multiple mutations that act together to prevent normal control of cell division. Proto-oncogenes are normal genes found in all cells that are important in controlling growth and development. Mutations in proto-oncogenes can convert them to oncogenes, which can transform normal cells into cancer cells. More than 60 oncogenes have been identified.
Cancer can result from the expression of active oncogenes and also from the inactivation of tumor suppresor genes (anti-oncogenes) that normally inhibit proliferation of transformed cells. A tumor suppressor gene that has been extensively studied is known as p53. Since its discovery in 1979, thousands of studies have been published about this gene, which appears to prevent the cell from copying damaged DNA. The p53 gene appears to be a key sensor that detects damage and then activates a gene circuit that controls apoptosis (self-destruction). Inactivation of the p53 gene (by mutation or indirectly by changes in other molecules with which it interacts) has been found in at least 50% of all human cancer cells. Cancers associated with p53 malfunction appear to be very aggressive, and investigators have suggested that the mutated gene may stimulate cell division instead of inhibiting it.
Cancer is the second greatest cause of death in the United States. One in three persons in the United States gets cancer at some time in his or her life, and two in three cancer patients die within five years of diagnosis. Currently, the key to survival is early diagnosis and treatment with some combination of surgery, hormonal treatment, radiation therapy, and drugs that suppress mitosis, such as chemotherapy. In patients with a functional p53 gene, radiation treatment and some forms of chemotherapy (e.g., tamoxifen) appear to work by activating the gene. Investigators are developing several approaches to p53-based cancer treatment. For example, viruses can be used to deliver functional p53 genes into malignant neoplasms. Another treatment approach that appears promising involves the use of immune therapy in which customized cancer vaccines destroy neoplasms.
Because cancer is actually an entire family of closely related diseases (there are hundreds of distinct varieties), it is probable that no single cure exists. The pace of cancer research has greatly increased with the recent application of a powerful new technique: microarrays. A microarray is a chip dotted with DNA from thousands of genes that can be used as probes to determine which genes are active in various types of cells including different types of cancer cells. This technique is being used to distinguish among cancer types and subtypes based on gene expression patterns. Different treatments might be effective for each subtype. For example, investigators might be able to determine which genes might be effective targets for treatment with a particular drug in each subtype of breast cancer.
Alleles of some genes appear to affect an individual's level of tolerance to carcinogens (cancer-producing agents). More than 80% of cancer cases are thought to be triggered by carcinogens in the environment.
Risk of developing cancer can be decreased by following these recommendations:
- Do not smoke or use tobacco. Smoking is responsible for more than 80% of lung cancer cases, and increases the risk for many other cancers.
- Avoid prolonged exposure to the sun. When in the sun, use sunscreen or sunblock. Exposure to the sun is responsible for almost all of the 400,000 cases of skin cancer reported each year in the United States.
- Eat a healthy diet including fruit and vegetables. Although research results are not clear, it appears prudent to increase the fiber content of your diet and avoid high-fat, smoked, salt-cured, and nitrite-cured foods.
- Avoid unnecessary exposure to x rays.
- Women should examine their breasts each month, have regular mammograms, and obtain annual Papanicolaou's (Pap) tests. Men should regularly examine their testes and should have prostate examinations yearly after age 50.
Nice article. I learnt a lot!! !!
ReplyDeleteThanks, Precious.
Glad you learnt a lot. Thanks Ebere
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